Photographs compress images of three-dimensional objects into flat, two-dimensional images displayed by a piece of paper, and television and motion pictures also compress images of moving three-dimensional objects into flat, moving, two-dimensional images displayed on a screen. Photographs, television, and motion pictures are examples of media that display three-dimensional objects as simply intensity mappings. In other words, when an image of a scene is ordinarily reproduced in a photograph or motion picture, a viewer does not see an accurate reproduction of the light scattered from the object, but instead a viewer sees a point-by-point record of just the square of the electromagnetic radiation amplitude reflected from the object (i.e., the irradiance). For example, the light reflected off a photograph carries with it information about the irradiance of the object displayed by the photograph but nothing about the electromagnetic wavefronts that were once scattered from the object during the taking of the photograph. As a result, a viewer only perceives a two-dimensional image of the object. Ideally, when the electromagnetic wavefronts scattered from an object can be reconstructed for a viewer, the viewer sees wavefronts that are indistinguishable from the wavefronts scattered from the original object. Thus, the viewer is able to perceives a reformed three-dimensional image of the object, as if the object was actually before the viewer.
Holography is a method of recording and showing a still three-dimensional holographic image of an object using a hologram and monochromatic light of a particular wavelength from a laser. A conventional hologram is a record of irradiance and wavefronts scattered from an object with respect to incident reference light. The hologram contains point-by-point information for reproducing a three-dimensional holographic image of the object, but is not an image of the object. FIG. 1A shows a conventional method for generating a hologram of an object 100. A laser 102 generates a coherent beam of light that is split by a beam splitter 104 to form an object beam and a reference beam. The object beam is reflected onto the object 100 by a mirror 106 and light scattered from the illuminated object 100 and the reference beam form an interference pattern on a photographic plate 108. The resulting interference pattern recorded on the photographic plate 108 is a hologram which contains the information used to reproduce the wavefronts of the object 100.
The hologram is used to reconstruct a three-dimensional holographic image of the object in approximately the same position that the object was in when it was recorded. FIG. 1B shows viewing a holographic image of the object 100. As shown in FIG. 1B, the laser 102 is positioned to illuminate a hologram 110 with monochromatic light stricking the hologram 110 at approximately the same angle as the reference beam. A viewer 112 looking through the hologram 110 sees a virtual holographic image of the object 100 suspended in space behind the hologram 110 in approximately the same position the original object 100 was in with respect to the photographic plate 108. The holographic image changes as the position and orientation of the viewer 112 changes. Thus the holographic image of the object 100 appears three dimensional to the viewer 112.
However, a hologram can only be used to produce a single still three-dimensional holographic image of an object. The systems used to generate holograms and holographic images are bulky, and the time and number of steps performed to produce a single hologram make current holographic methods and systems impractical for producing three-dimensional motion pictures of objects. In addition, the three-dimensional holographic images are typically monochromatic because light of a single wavelength is often used to generate the holographic image. Thus, it is desirable to have holographic methods and compact holographic systems that enable the production of three-dimensional color holographic images and color holographic motion pictures.